Process of heat-treating metal



gmnntoc /J/w ///.//////,M

J J BOWDEN PROCESS OF HEAT TREATING METAL e@ WJ E im@ (i .Patented Sept. 29, 193i `UNITED STATES PATENT OFFICE I JAMES J'. BOWDEN, OF TVARRIEN,l O HIO PROCESS OF HEAT-TREATING METAL Application led Deoember 29, 193i). Serial No. 505,353.-

material for the manufacture of metal prodv ucts. This process is intended more especially .for use in heat treating large charges where absolute evenness of treatment is not indispensable but where high grade and uniform quality is desirable. In

' the past the trade has been forced' to tolerate a rather inferior type of heat treatment because uniformity and high quality could not be economically secured by the employment of known methods. Box annealing has been carried out byr placing the charge, often several tons, in a heavy cast iron or similar heavy metallic'annealing box, inserting said box into a' furnace where the jlames and products of combustion are brought into direct contact therewith. The construction of furnaces used in this process have not led to uniform temperaturesr in all parts of the charge.

The principal object of my invention is to provide aprocess for heat treatin "large charges which will result in the pro uction of a more nearly uniformly treated and therefore superior product, a saving of fuel,-

a greater simplicity and nicety of-tempera- Y ture control and a saving in the time required tf carry out the process. More limited objects of myinvention are to combinel .the features ofA exclusion of air from the' charge of metal to be treated with `that of preventing access to such charge of the material which is employed for transmitting heat thereto, to reduce tov a minimum the amount of heating material required while jtemperatures until the desired temperature means indicated at H. Each vatlis to contain a molten material which at its melting point will have a temperature substantially lower than that to which the charge of material to be treated is desired to be brought. Such molten material mayl consist of any one ofa large number of salts, such, for example, as sodium carbonate, sodium chloride, sodium hydroxide, sodium sulphate, in fact,

the common salts or compounds of potasv sium, calcium, sodium, barium, bismuth and magnesium. I may also employ molten metals, 'such as lead, tin, zinc, copper, etc.

In its simplest aspect, as shown in Fig. 2 of the drawings, my improved method will consist in immersing the annealing box A containing the charge C of metal to be annealed in the molten liquid L, allowing it to remain there until it assumes the desired temperature, preferably substantially that of the liquid L, and then subjecting to any typefof cooling desired tobring out the particular characteristic of the ymetal which is to be secured. The apparatus illustrated may be employed for the cooling treatment 7 or additional apparatus may be used. The.

container A will preferably consist of an iron or steel receptacle.

By the use o'f a plurality of vats, each containing a different molten liquid, it is possible to secure a number of diierent temperatures by the simple expedient of removing the annealing box from one vat to the other. In this Way, I am enabled to subject the charge to gradual heating and gradual cooling, to retain the same at substantially any temperature for as long as maybe required, and to reduce the capacity of each yvat very considerably Without excessively lowering the temperature of the }liquid L, which might result in the undesirable effect of freezing the liquid, by the simple expedient Vof immersing the annealing box-in solutions of successively higher A' A very important feature of my invention is the sealing of the charge in the air-tight and liquid-tight annealing box A before it Iis immersed in. the heatng'liquid and se- 100 curing the double function of excluding the charge from atmosphere and the surrounding heating medium. It is to be noted that various mixtures may be used to secure various melting temperatures of the liquid L; For example, a mixture of soda ash and sodium hydroxide or a mixture of copper and tin, lead and tin may be employed. The proper 'control of the temperature is quite important since a number of metals, suchas iron, steel, brass, zinc, aluminum, etc., have critical temperatures at which various metallurgical changes in structural composition occur.

Having vthus described my invention, what I claim is:

1. The method of heat treatment which consists in enclosing the char e to be treated -in an air-tight and liquid-tight container,

immersing said container with its contained charge in a molten heating agent and allowing it to remain so immersed until the charge assumes substantially -the temperature of said molten heating agent.

2. The method of heat treating metal f v which consists in enclosing a charge of the metal to be treated in a container, submerging said container vwith its contained charge in amolten heating agent'and allowing it to remain therein i1nt1lthe desired metallurgical efect has been secured, said container being of such construction as4 to prevent the entrance thereinto of said heating agent.

3. The method of heat treating metal which consists in enclosing a chargel of the metal to be treated in a substantially airtight and liquid-tight container, at least partially covering said container with its contained charge with a molten heating agent and allowing it to remain therein until the desired metallurgical effect has been secured. i

In testimony whereof, I hereunto aiix my signature.

JAMES J. BOWDEN. 

